This project will investigate the novel use of stereotactic radiotherapy (ionizing radiation under stereotactic guidance) for the treatment of pediatric and adult astrocytomas. This technique couples the biological advantages of fractionation used in conventional radiotherapy with the highly precise and focal dose distribution produced by stereotactic radiosurgery. Our ability to perform stereotactic radiotherapy is related to two recent developments at the Brigham and Women's Hospital and the Children's Hospital: 1) a dedicated stereotactic radiotherapy facility with a specially designed, stereotactic linear accelerator, and a stereotactic radiation physics facility, 2) the design of a relocatable, non-invasive stereotactic headframe that will allow for daily, fractionated treatments with excellent precision (daily set-up error < 1 mm). Local control remains a major obstacle in the successful treatment of astrocytomas. Attempts to increase the radiation dose with conventional techniques have failed to improve survival because of the development of irreversible, diffuse brain injury. Because of the sharp dose gradient produced at the field edges with stereotactic radiotherapy, we will be able to significantly escalate the dose of radiation delivered to the target region while minimizing the dose delivered to the surrounding brain. This project will examine the effects of radiation dose optimization and escalation on survival in children and adults with incompletely resected astrocytomas. We will also examine and characterize the patterns of failure seen following escalated doses of highly focal stereotactic radiotherapy.